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Article

Mineral Condition Changes in Amended Soils and Woody Vegetation Installed on a Polluted Soil with Trace Metals in Lubumbashi (DR Congo): Results of a Four-Year Trial

by
Serge Langunu
1,2,*,
Jacques Kilela Mwanasomwe
1,
Dieu-donné N’Tambwe Nghonda
1,3,
Gilles Colinet
2,* and
Mylor Ngoy Shutcha
1,4
1
Ecology, Ecological Restoration and Landscape Unit, Faculty of Agronomic Sciences, Université de Lubumbashi, Lubumbashi 1825, Democratic Republic of the Congo
2
Water-Soil-Plant Unit, TERRA Gembloux Agro-Bio Tech, University of Liege, 5030 Gembloux, Belgium
3
Biodiversity, Ecosystem and Landscape Axis, Gembloux Agro-Bio Tech, University of Liège, 5030 Gembloux, Belgium
4
Plant Ecology and Biogeochemistry, Université Libre de Bruxelles, 1050 Bruxelles, Belgium
*
Authors to whom correspondence should be addressed.
Environments 2025, 12(7), 224; https://doi.org/10.3390/environments12070224
Submission received: 21 May 2025 / Revised: 22 June 2025 / Accepted: 23 June 2025 / Published: 30 June 2025
(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Soil Contamination and Remediation)
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Abstract

The use of trees to revegetate urban areas contaminated by mining activity is a low-cost, low-maintenance technique, of which the success will depend on the plant species, planting methods, and geochemical processes at the soil-plant interface. This study analyzed the evolution of mineral composition in the rooting soil, tree, and herbaceous vegetation on soils contaminated by As, Cd, Cu, Co, Pb, and Zn. An in-situ experiment was carried out in Lubumbashi (South-eastern DR Congo) with six tree species (Acacia auriculiformis, Albizia lebbeck, Delonix regia, Leucaena leucocephala, Mangifera indica, and Syzygium guineense), in 0.187 m3 pits amended with municipal compost and limestone. After planting in the amended and unamended (control) pits, soil samples were taken for chemical analysis. Eighteen months after planting, a floristic inventory was carried out to assess the spontaneous colonization of herbaceous species. The results show an increase in metal concentrations in the rooting soil between 2019 and 2023 (Cu: 725 ± 136 to 6141 ± 1853 mg kg−1; As: 16.2 ± 1.4 to 95 ± 28.5 mg kg−1; Cd: 2.7 ± 1.3 to 8.7 ± 2.0 mg kg−1; Co: 151 ± 36.3 to 182 ± 113 mg kg−1; Zn: 558 ± 418 to 1098 ± 1037 mg kg−1), with a stable pH and a decrease in nutrients (P, K, Ca, and Fe). The trees planted in the amended pits showed better height and diameter growth and greater survival than the controls, reaching average heights of 8 m and a DBH of up to 22 cm four years after planting. A total of 13 spontaneous herbaceous species were recorded, with an increased abundance during the second inventory. These results confirm the effectiveness of pit amendment for the rapid revegetation of urban soils polluted by trace metals.

1. Introduction

Soil pollution by trace metals is a recurring environmental problem in urban areas throughout the world, particularly in industrial regions or mining areas [1,2]. This pollution has harmful effects on ecosystems and human, animal, and microbial health, as well as on plant health [3,4]. For example, these effects can lead to respiratory and cardiovascular diseases, reproductive disorders, cancers, and impaired cognitive development in humans [5,6] and can also affect plant nutrition, reducing growth and development [7].
In sub-Saharan Africa, in the south-eastern region of the DRC, more specifically in the Katangan Copperbelt (KCB), hills enriched in Cu and Co outcrop at the surface and host a unique metallophytic flora with nearly 600 metallophytes [8,9]. Mining activities in this region date back more than a century [10] and have left visible traces, particularly bare patches of soil allowing the dispersion of contaminated particles by water erosion in the rainy season and wind erosion in the dry season into other environmental compartments (air, garden soil, surface, and groundwater) [11]. Recent studies in the region have demonstrated the negative impact of mining activities on soils [12,13,14] surface water, and groundwater [15,16], with considerable repercussions for the food chain and people’s health [17,18,19].
For all these reasons, soil remediation is essential to combat this pollution. The remediation process consists of eliminating, reducing, or mitigating polluted and destroyed soils using biological and physicochemical techniques [20]. Biological remediation methods, such as phytoremediation, are more effective and environmentally friendly [21]. Phytoremediation uses plants (both accumulators and non-accumulators) to remediate soils contaminated with trace metals, offering a cost-effective and environmentally friendly solution [22,23]. However, revegetating soils polluted with trace metals is a difficult task because the edaphic conditions (low fertility, low pH, low OM content, low CEC, etc.) are not conducive to plant growth. Trees, in particular, are known for their ability to improve soil quality by absorbing various elements [24,25]. Their root systems secrete enzymes that facilitate the absorption of nutrients into the soil, thereby contributing to the dynamics of mineral conditions in the rhizosphere, the zone of the soil influenced by the presence of plant roots. Because of the uptake of metals by roots, the rhizosphere is often more concentrated in trace metals than other parts of the soil [26]. This can significantly influence tree growth and the establishment of sustainable vegetation [27].
In this context, studying changes in soil mineral composition in the root zone and the growth of plants established on metal-polluted soils becomes crucial for an in-depth understanding of the processes that influence their development. This approach provides a better understanding of the factors that regulate plant growth and changes in soil mineral composition. It is proving useful in identifying the tree species best suited to specific environmental conditions, as well as in conserving biodiversity and making decisions about the management of polluted land [28]. In Lubumbashi in particular, the area exposed to the south-easterly trade winds from the metal plant has soils with exceptionally high concentrations of copper (>30,000 mg·kg−1) and other metals (Cd, Co, Pb, and Zn). As a result of these activities, the original Miombo forest has disappeared, leaving bare soil surfaces subject to erosion [29,30].
To contain this contamination, efforts have been made to revegetate the bare soil with trees. The operation involves excavating contaminated soil and replacing it with non-contaminated soil improvers [31,32]. Encouraging results have been obtained as this approach appears to be effective while offering less risk of contamination for crop products [32]. In addition, this method encourages the spontaneous establishment of herbaceous vegetation that provides year-round soil cover in the corridors of planted trees, thereby preventing erosion [33]. However, despite these advances, no study has evaluated the monitoring of the mineral composition of the root growth zone, the growth dynamics of the trees, or the timing of the appearance of herbaceous plants via experimental plantations on polluted soil. Therefore, obtaining primary data on soil mineral composition and tree survival and growth is essential for developing predictive models for the evolution of woody cover to propose large-scale remediation. In addition, these models can be used to assess environmental impacts, such as climate change or ecosystem rehabilitation [25,27].
Approaches to monitoring tree growth dynamics are based on various methods such as dendrometric measurements, an analysis of annual rings, photosynthesis monitoring, sap flow measurements, remote sensing, and modeling [34,35]. The choice of monitoring method depends on the objectives of the study. In this study, direct dendrometric measurements, which measure tree height and diameter, were chosen for their ability to provide precise and accurate data on tree growth over time.
The general objective of this study was to show the evolution of the mineral composition of the soil and woody vegetation on soils heavily polluted with metals. More specifically, we (i) assessed the dynamics of mineral conditions in the root growth zone of woody plants in the medium-term (4 years) and (ii) assessed the dynamics of vegetation established on contaminated soils, including woody plants and herbaceous plants. The results of this study will be of crucial use in guiding decisions on the large-scale remediation of soils polluted with trace metals in Lubumbashi and elsewhere.

2. Materials and Methods

2.1. Study Site

The study was carried out in the city of Lubumbashi, specifically on the grounds of the Gécamines-Sud hospital in the Penga Penga district (11°40′42″ S latitude, 27°27′56.50″ E longitude, elevation 1215 m) (Figure 1). At this site, the trial was set up on a rhodic allisol [36] subject to polymetallic contamination, with particularly high concentrations of Cu (>17,000 mg·kg−1), but also of As, Cd, Co, Pb, and Zn when compared to uncontaminated soils in the region [37]. The city’s climate is of the Cw type, characterized by the alternation of a well-defined dry season (May to September) and a rainy season (November to March), separated by two transitional months (April and October) [38]. Annual rainfall varies between 1200 and 1300 mm, and the average annual temperature is 20 °C [39].

2.2. Plant Material

Six woody species, belonging to four families (Table 1, Figure 2), formed the biological material for the present study. These species were selected based on their tolerance to trace metals, their rapid growth, and their high biomass production, coupled with their deep root system and the edible nature of their fruit. They generally reach heights of 10–25 m in normal, uncontaminated soil. Except for M. indica, the other woody species have already been used to rehabilitate soils polluted with trace metals by mining activities [40,41,42,43].

2.3. Experimental Plot

A random block layout with a factor (municipal compost + limestone × species) covering an area of 0.27 ha was installed. Planting pits measuring 0.187 m3 (0.50 m wide × 0.50 m long × 0.75 m deep) were dug in this area at a spacing of 5 m × 5 m (Figure 3). Each pit was filled with a mixture of 350 kg of municipal compost and 6 kg of dolomitic limestone (CaCO3, MgCO3) containing 52% Ca and 25% Mg. The municipal compost came from the public landfill on the Lubumbashi University campus, and its characteristics are given below (Table 2). The dolomitic limestone came from the Likasi limestone quarry. Municipal compost and limestone were used as amendments in the restoration of contaminated pits due to their effectiveness in improving the physico-chemical properties of degraded soils. The compost provides essential nutrients (N, P, and K), increases organic matter content, stimulates microbial activity, improves soil structure, and reduces the bioavailability of trace metals through complexation mechanisms. Limestone was primarily applied to correct soil acidity, common in the study area, by raising the pH to levels favorable for plant growth while immobilizing trace metals through precipitation reactions, thereby limiting their mobility and toxicity. Moreover, the use of municipal compost aligns with a circular economy approach by valorizing abundant urban waste in the region, contributing to urban sanitation, and reducing rehabilitation costs for contaminated soils, as well as affordability (low cost) for the population who may wish to plant trees on their residential properties.
After the addition of amendments, a period of 30 days was observed before planting. Finally, six woody species were planted, totaling 115 individuals, distributed as follows: A. lebbeck (26 individuals, including 21 in amended pits and 5 in non-amended pits), S. guineense (26 individuals, including 21 in amended pits and 5 in non-amended pits), A. auriculiformis (29 individuals, including 25 in amended pits and 4 in non-amended pits), L. leucocephala (8 individuals, equally distributed between amended and non-amended pits), D. regia (13 individuals, including 9 in amended pits and 4 in non-amended pits), and M. indica (13 individuals, including 9 in amended pits and 4 in non-amended pits). In total, 89 seedlings were planted in amended pits and 26 in non-amended pits. This experiment was conducted during the rainy season, from November to December 2019. To ensure proper seedling establishment, supplemental irrigation was provided during the first dry season following planting. Moreover, the unequal number of individuals between the amended and unamended pits is due to a pre-selection carried out during preliminary studies conducted under controlled conditions [42,46].

2.4. Plantation Monitoring and Species Inventory

In this study, we assessed plant survival and growth (height) at regular intervals throughout the experimental period (50 months), starting when the plants were planted. To obtain the survival rate, the number of individuals alive at the last sampling was divided by the total number of individuals initially planted, multiplied by 100. We also measured the height of the plants every six months over the four years to determine their growth over time. To classify the stand into diameter classes, the diameter at breast height (DBH) of all surviving individuals was measured in cm at 1.3 m above the ground using a forest tape, while height was measured in meters using a SUUNTO clinometer [47,48]. Juvenile trees from the regeneration of initially planted species were counted systematically, and flowering and fruit production were monitored.
To assess the spontaneous establishment of herbaceous species, they were characterized using the Braun–Blanquet phytosociological abundance-dominance method [49]. The floristic inventory was carried out using well-defined 5 m × 5 m (25 m2) quadrats [50] in which herbaceous species were counted and identified at two different times (2021 and 2023).

2.5. Chemical Analysis

Samples were taken before the trial was set up and three years after planting directly in the root growth zone to assess changes in soil mineral composition over time. A soil probe was used to take samples from a depth of 0 to 30 cm. These samples were dried at room temperature (<35 °C) and sieved to 2 mm, and a sub-sample was ground to 200 µm to enable fine analysis of the mineral composition of the soil. It should be noted that chemical analyses were conducted only on amended soil samples (n = 10). Non-amended soils were sampled and analyzed before the implementation of the experiment (i.e., before pit amendment and planting) and served as the initial baseline for comparison (Table 2).
The chemical analysis methods were described by Lienard and Colinet [51]. Soil pH was measured potentiometrically in a 1:2.5 (w/v) suspension in water and 1N KCl, while total organic carbon (TOC) was determined using the Springer–Klee method. Concentrations of the major elements (Ca, Mg, K, and P) and trace elements (Fe, As, Cd, Co, Cu, Pb, and Zn) were determined after (a) extraction with CH3COONH(4) (0.5 M) and EDTA (0.02 M) at pH 4.65 (w/v ratio 1:5) and stirring for 30 min (concentration of available metals), and (b) digestion with aqua regia according to ISO 11466 (concentration of total metals), respectively [52]. Concentrations in the solutions were measured by flame atomic absorption spectrometry (AAS, Varian 220, Agilent Technologies, Santa Clara, CA, USA) for major elements, except P (colorimetry), and by ICP-OES for metal content in aqua regia.

2.6. Statistical Analysis

The Chi-square test (χ2Pearson) was used to compare the survival of individuals between the two soil types. A normality test was applied to the data on woody growth parameters. As the distributions were not normal, even after transformations, the non-parametric Kruskal–Wallis (KM) test was used to compare plant height and diameter at breast height (DBH). The relative abundance of the species richness of spontaneous herbaceous species in the tree corridors was determined after transforming the Braun–Blanquet coefficients into percentages. The relative abundance of species was calculated by dividing the number of individuals of the species by the total number of individuals of the species multiplied by 100. All the analyses were carried out using R Studio software (version 4.0.3).

3. Results

3.1. Dynamics of Mineral Composition in Soils over Four Years

The pHKCl values of the surface soil horizons of the species studied do not show any major variations between 2019 (7.2 ± 0.03) and 2023 (7.2 ± 0.2), in contrast to the variations observed for the other fertility parameters (Table 3). There was a downward trend in Ca, Fe, P, and K values, but an increase in Mg values (Table 3). In particular, concentrations fell by a factor of 2.5 for P (1327± 688 vs. 516 ± 71.0 mg kg−1) and 1.8 for Ca (21,797 ± 10,862 vs. 12,262 ± 6062 mg kg−1), while they increased on average by a factor of 1.2 for Mg (2791 ± 871 mg kg−1 to 3550 ± 695 mg kg−1).
Concerning trace metals, a general trend of increasing concentrations was observed between 2019 and 2023 (Table 4). The greatest average increase in concentrations was observed for Cu, with values in 2023 (6.141 ± 1.853 mg kg−1) eight times higher than those in 2019 (725 ± 136 mg kg−1). After Cu, the increase factors were higher for As and Pb, with concentrations in 2023 six times higher than those observed in 2019 (As: 16.2 ± 1.4 mg kg−1 in 2019 vs. 95 ± 28.5 mg kg−1 in 2023; Pb: 62 ± 32 mg kg−1 in 2019 vs. 421 ± 160 mg kg−1 in 2023). Cd concentrations observed in 2023 are three times higher on average (2.7 ± 1.3 mg kg−1 in 2019 vs. 8.7 ± 2.0 mg kg−1 in 2023), while they are less than twice as high for Co (151 ± 36.3 mg kg−1 in 2019 vs. 182 ± 113 mg kg−1 in 2023) and Zn (558 ± 418 mg kg−1 in 2019 vs. 1098 ± 1037 mg kg−1 in 2023).

3.2. Vegetation Dynamics Between 2019 and 2024

3.2.1. Survival Dynamics, Growth, Reproduction, and Regeneration of Woody Species

The results showed that none of the trees in the untreated pits survived to March 2024, i.e., after 50 months of cultivation. In contrast, the survival rate of trees planted in amended pits was 87.6% (78 out of 89 individuals). In the case of individuals planted in amended pits, mortality was mainly observed after the first dry season in 2020. To mitigate early transplant stress and promote establishment, supplemental irrigation was applied during this initial dry period, which likely contributed to the overall success observed in the amended plots. Individuals who survived the first dry season remained alive until the last measurement in March 2024. The highest survival rate was obtained for A. lebbeck, D. regia, and L. leucocephala with 100% survival each, followed by S. guineense with 90%. Low survival rates were observed for A. auriculiformis and M. indica, with 72% and 77%, respectively. Individuals planted in the pits amended in 2019 reached average heights ranging from 3.0 to 8.6 m in 2024 (Figure 3). The general trend of the curves presented in Table 4 shows an acceleration in the increase in height during the second year of growth. However, a variation in the rate of growth in height was observed between species, characterized by differences in the value of height reached after four years of cultivation. In 2024, individuals of L. leucocephala reached a higher average height (8.6 ± 0.16 m) than the other species (p < 0.05). They were followed by A. auriculiformis (6.4 ± 0.38 m) and S. guineense (6.1 ± 0.23 m). The slowest growth rates in height were observed for D. regia and M. indica, which reached heights of 3.2 ± 0.22 m and 3 ± 0.8 m, respectively. Most of the species appear to be promising for reforestation or ecological restoration projects because of their faster development in specific environmental and edaphic conditions. The performance of these six species in uncontaminated environments is given for comparison. Species such as L. leucocephala (14.53 m tall and 14.26 cm in diameter) and A. auriculiformis (14.16 m tall and 8.52 cm in diameter) show strong growth, while D. regia and M. indica show weak growth (5.2 m and 5.1 m, respectively) compared with A. lebbeck (9.45 m tall and 8.14 cm in diameter) and S. guineense (8.76 m tall and 8.2 cm in diameter), which show intermediate growth (Table 5). Although the durations are not the same, the performance of the trees in the plantation pits seems acceptable.
Environments 12 00224 g003
Figure 3. Growth in height of the six woody species grown in the trial over 50 months.
Figure 3. Growth in height of the six woody species grown in the trial over 50 months.
Environments 12 00224 g003
The DBH values in 2024 range from 2.1 to 21.6 cm for all species combined. The diameter structure of the woody stand in 2024 (Figure 4 and Figure 5) shows a greater contribution from the youngest classes (<10 cm), with 51 individuals, or 65.3%. If the 10–15 cm classes are included, the number of individuals rises to 73, representing 93.5%. The 15–22 cm classes represent only 5 trees, or 6.5%. The distribution of diameters is not uniform between species. DBH classes 16–22 are only represented by individuals of A. lebbeck and S. guineense, while all D. regia and M. indica individuals had DBH < 10 cm in just over four years. The KW test indicated that there was a significant difference in DBH in 2024, with higher mean values for L. leucocephala (10.3 ± 3.4 cm) and A. lebbeck (10.2 ± 4.6 cm). These two species were followed by S. guineense (8.4 ± 3.5 cm) and A. auriculiformis (8.2 ± 2.4 cm), while the lowest values were observed for D. regia (4.9 ± 2.2 cm) and M. indica (4.9 ± 0.6 cm).
Figure 6 shows the results of the relationship between tree frequency and diameter at breast height (DBH) for each species. A diversity of species can be observed with significant variations in terms of frequency and growth, which could indicate varied adaptations. A. auriculiformis and A. lebbeck are frequent with moderate to high DBH. D. regia and M. indica are less frequent and have a smaller DBH, while S. guineense is the most frequent. In terms of comparison between species, A. lebbeck has the widest range of DBH, suggesting that it can grow over a wider range, while S. guineense is the most widespread species; it does not reach DBH values as high as those of A. lebbeck. The other species have a moderate frequency and DBH distribution.
The time from planting to flowering was not uniform for the six species grown in the trial (Figure 7). Flowering and fruit production were observed from the third growing season for L. leucocephala, the fourth growing season for A. lebbeck and D. regia, and the fifth growing season for A. auriculiformis and S. guineense. No flowering was reported for mango individuals until the end of the observations (March 2024).
A total of 98 new individuals from natural germination (height > 30 cm) were observed at the end of the 2023–2024 season. Two species contributed most to the number of juveniles recorded: L. leucocephala with 79 individuals (80.6%) and A. lebbeck with 19 individuals (19.4%). However, many germinations were observed with seedlings at the 3 to 4-leaf stage for A. auriculiformis, A. lebbeck, and L. leucocephala.

3.2.2. Dynamics of the Herbaceous Layer

A total of 13 spontaneously established herbaceous species were identified since their appearance during the 2020–2021, 2021–2022, 2022–2023, and 2022–2024 growing seasons (Table 6). These species were observed at the base and/or 1 m from the trees in the amended areas and also between the corridors. Bulbostylis pseudoperennis, Microchloa cupricola (Rendle) Stapf, Imperata cylindrica (L.) P. Beauv, Celosia trygina L., and Setaria pumila mainly established themselves on the unamended soil of the corridors formed by the lines of the ligneous plantations. These species were all observed at the end of the first year of cultivation in 2020. Ageratum conyzoides L., Euphorbia hirta L., and Tithonia diversifolia (Hemsl.) became established during the second growing season (in 2021). Crassocephalum rubens (Jus. Ex Jacq.), Cynodon dactylon (L.) Pers, Nicandra physaloïdes (L.), and Panicum maximum Jacq. became established during the 2022–2023 season, mainly in the amended growing halos of woody species.
B. pseudoperennis and M. cupricola were the most abundant species. The cover change was in favor of M. cupricola between the observations made in March 2021 and those made in March 2023, with 68.6% compared with 48% for B. pseudoperennis. Except for I. cylindrica (19%), the other species had overlap values of less than 10% during the last observation season. Across the system as a whole, ground cover by these spontaneously established herbaceous plants was in the region of 65 to 80% (Figure 8).

4. Discussion

4.1. Dynamics of Mineral Composition in the Soil Around Trees over Time

Observations made in previous studies on plantations over 15 years old showed high concentrations of metals (As, Cd, Co, Cu, Pb, and Zn) in the amended soil of trees planted at Penga Penga [32] and in the Kipushi sedimentation basin [43]. To explain this situation, and based on the literature [28], the hypothesis of enrichment due to lateral transfers from surrounding polluted soils was put forward. The results of the present study support this hypothesis based on the dynamics of metal concentrations in the root growth horizon during the observation period from 2019 to 2023. Indeed, a significant enrichment of metals was observed in the restored pits, particularly for copper (Cu), whose concentration in 2023 was eight times higher than in 2019 (Figure 4). This trend is also evident for elements typically scarce in the region’s soils, such as arsenic, cadmium, and lead, supporting the hypothesis of external inputs, notably from the heavily contaminated soils of Penga Penga [12,37,54]. These findings indicate that such enrichments can occur over a relatively short period. The organic amendments used, especially municipal compost, influence the soil’s chemical composition. Their heterogeneity, stemming from the nature of inputs and processing methods, can lead to either the introduction or stabilization of trace metals [55]. Some amendments add trace metals, while others stabilize contaminants by improving soil structure and nutrient availability [56]. In the former case, metals such as Cu, Zn, or Pb may be directly introduced through amendments [57,58].
Furthermore, the improved soil structure resulting from these amendments enhances the retention of fine particles and organic matter, facilitating the lateral migration and accumulation of metals from surrounding soils enriched in Cu and other metals due to industrial activities, particularly from the Gécamines copper smelting plant [32,59,60]. Ref. [43] reported a significant increase in Cu and Co concentrations in amended layers compared to tailing soil layers in the experimental trial with tree species on mine tailings. Biological processes also play a crucial role in this dynamic. Root activity and organic matter decomposition alter rhizosphere conditions, promoting the remobilization of adsorbed metals. Root exudates can release chelating agents, thereby increasing the solubility and bioavailability of metallic elements [61,62,63]. These physicochemical and biological interactions contribute to the observed reconcentration of metals, particularly Cu, in the planting pits after four years.
Alongside this accumulation of trace metals, a decline in concentrations of essential macroelements was observed, reflecting a gradual deterioration in soil fertility conditions (Figure 5). There are several possible explanations for this decline. Firstly, the increase in metal concentrations disrupts the soil’s biological balance and reduces the availability of nutrients for tree roots, a phenomenon that has been widely documented [55,56,61]. On the other hand, leaching and erosion processes seem to be exacerbated by the youth of the plantation. The root system, which is still not very dense or extensive, does not effectively stabilize the soil, which encourages nutrients to migrate to deeper horizons or less concentrated neighboring areas.
An additional factor of observed variability lies in the organic amendments used, whose influence on the success of phytoremediation is well documented [11,64]. Depending on their composition and degree of stabilization, soil improvers influence the dynamics of metals and nutrients in different ways. For example, compost rich in humified organic matter plays a stabilizing role by limiting the bioavailability of metals and improving soil structure. Conversely, less stabilized compost can rapidly release nutrients, but its beneficial effect remains limited over time due to its rapid biodegradation. The heterogeneity of the effects observed between the different plots at Penga Penga therefore suggests that the quality of the soil improvers and how they are applied must be rigorously optimized to ensure the long-term success of phytoremediation. Despite the reduction in nutrients, their concentrations in the amended zone remain higher than those in the surrounding soil (Table 3), enabling the trees to maintain healthy growth. A key factor explaining this resilience is the neutral pH observed in the amended soil (Table 3), which favors the availability of nutrients to plants, even in soil heavily polluted with trace metals. This pH stability could be the result of the interaction between the organic matter from the soil improvers and the biological activity of rhizospheric micro-organisms, helping to buffer the pH variations often observed in contaminated soils [65,66,67].
All these observations underline the need to adopt appropriate strategies to maximize the effectiveness of soil improvers and guarantee the optimum development of phytostabilisation trees. It seems essential to favor stabilized soil improvers rich in organic matter, such as well-matured composts, which promote nutrient retention while reducing the bioavailability of trace metals [68,69]. In addition, the application of soil improvers needs to be carefully adjusted according to soil properties and local environmental conditions, to limit the risks of leaching and erosion [70]. An approach combining organic amendments and complementary techniques, such as the introduction of symbiotic microorganisms (mycorrhizae, growth-promoting bacteria), could prove particularly effective in improving plant resilience to metal contamination [70,71,72]. In addition, it would be important to consider the variability of soil and environmental conditions, given that the effect of amendments varies according to soil texture, rainfall, and the initial composition of the substrate.

4.2. Medium-Term Plantation Dynamics

The planting of trees on metal-contaminated soils generally fails due to a lack of knowledge about the factors that stimulate their growth and development [73]. The choice of plant species, amendments, planting techniques, and climate are the limiting factors for plant development [74,75,76]. The results of this study are a first for the Katangan copper arc region, with systematic monitoring from the time the experiment was set up through to its medium-term follow-up. The conclusions of previous studies [31,32,33,77] presented interesting prospects for the implementation of trees in remediation strategies based on the excavation of contaminated soils by replacing uncontaminated substrates with mine tailings and soils polluted with trace metals. The results of this study confirm the success of this technique in terms of tree survival and growth. It can be seen that the planted trees reached heights of up to 8 m in a relatively short space of time (Figure 5).
Despite the tendency for metal concentrations in the planting hole to increase, better survival was observed 4 years after planting. This is evidenced by better growth in height and diameter for most species. Indeed, it has been shown that some tree species can survive and develop in soils contaminated by trace metals, despite high soil concentrations [78,79]. This ability to survive at high metal concentrations is perhaps due to their capacity to avoid, absorb, or transfer metals efficiently in their plant tissues [80], but also the fertility conditions observed in the soil (Table 3). Except for M. indica, the other five tree species used in this study have already demonstrated their ability to grow on mine tailings and soils polluted with trace metals by mining activities around the world [40,41,46].
The results relating to the diametric structure of the stand in this study show a distribution of trees by diameter class in an inverted “J” shape (Figure 4). This pattern indicates that there are many small-diameter trees and few large-diameter trees, indicating a stand in full regeneration and growth [81]. It has been established in the literature that a stand with such a structure can develop and grow plants over time [82]. This thesis is supported by the number of individuals who appeared in this trial. For example, A. auriculiformis had a large number of regenerating (+700) young plants at the three- to four-leaf stage, and L. leucocephala was the species that showed the largest number of juveniles that were less than 30 cm tall. On uncontaminated soils, the species studied are characterized by rapid growth and high regeneration potential, reaching heights of up to 20 m in 6 to 8 years [83,84,85]. At four years, they were between 3.0 and 8.6 m tall and had diameters ranging from 4.9 to 10.3 cm, confirming their vigor and sustained growth (Table 6). These results are comparable to those reported by Gnahoua et al. [53] and Numbi et al. (in press), who observed in Côte d’Ivoire and the DRC, respectively, that individuals of A. auriculiformis, A. lebbeck, L. leucocephala, D. regia, M. indica, and S. guineense reached heights of 5.20 to 14.53 m and diameters of 5.6 to 14.26 cm at six years of age in uncontaminated soils. These growth rates are consistent with those reported in other regions with similar ecological conditions. In India, for example, A. lebbeck is known for its rapid growth, reaching 18 m in height and 66 cm in diameter in 10 years in unpolluted soil [40]. In the Philippines, L. leucocephala shows an annual growth rate of 2.5 m in height and 5 cm in diameter, reaching 20 m in just 8 years (NAS, 1984, cited by [53]. These results confirm the high potential of these species for reforestation and phytoremediation in tropical environments.
Overall, these tree species can help restore degraded ecosystems because of their ability to fix atmospheric nitrogen in the soil and improve overall soil quality [86,87,88]. However, M. indica showed a relatively low growth rate compared with other species under the same conditions. This difference in growth can be explained by the intrinsic factors of the species, but also by competition for resources with the other species. The mango tree needs resources such as water, nutrients, and light to grow and prosper, but in situations of competition with other species, as in this study, the mango tree may grow more slowly [89].
In addition, the difference in growth observed between species is also reflected in the dynamics of the speed of flowering and fruit production. It can be seen (Figure 7) that the species entered flowering at different times. This differentiation can be explained by genetic codes and intraspecific variability, but also by environmental conditions, particularly competition for nutrients and light [90]. These results suggest that the remediation technique based on excavation/replacement by municipal compost followed by planting is a good approach for rehabilitating soils polluted by trace metals [55], but it is important to monitor the increase in metal concentrations in the amended zone to reduce the risk of contamination of the food chain through the accumulation of metals in plant shoots. In addition to growth-related findings, it is important to highlight the potential risk of metal uptake by plants, particularly for the fruit-bearing species studied here. The transfer of contaminants to edible plant parts raises significant food safety concerns, justifying targeted analyses of fruits to assess potential health risks. In this regard, the studies by [76,77] have already documented metal concentrations in various plant compartments, including fruits, leaves, and wood.
In addition, this remediation technique made it possible to trigger facilitation processes for the colonization of herbaceous species in this type of environment [33]. The trees used acted as nurse plants, encouraging the colonization of herbaceous metallophytes and/or non-metallophyte species. In fact, by modifying the soil conditions in their zone of influence, the planted trees created a microclimate that favored the establishment or spontaneous propagation of B. pseudoperennis, M. cupricola, I. cylindrica, C. trigyna, T. labialis, C. dactylon, E. hirta, N. physaloïdes, T. diversifolia, P. maximum, A. conyzoides, and C. rubens (Table 6). In addition, this spontaneous colonization of herbaceous species can be attributed to three main factors: firstly, there was an improvement in edaphic conditions with the addition of municipal compost, which enriched the soil in nutrients and improved its structure, thus creating a favorable environment for the germination and growth of herbaceous species [91,92]. Secondly, the presence of a seed bank in the soil and municipal compost meant that, as conditions improved, these seeds germinated and colonized the area. Finally, the dispersal of seeds carried by wind, animals, and human activity from surrounding areas favored the establishment of new herbaceous species [91,93].
In addition, these species had different appearances and growth dynamics depending on the growing season. Some groups appeared one year after planting, while others appeared in the fourth year. Similar observations were made by Mwanasomwe et al. [33], who observed a high relative abundance of spontaneous colonization of herbaceous and even woody species in a mine tailing remediation trial 15 years after planting. Boisson et al. [94] noted that the installation of a pioneer plant in phytostabilization trials favored the emergence and survival of two cupricolous species in the Katangan Copperbelt. Indeed, the richness of herbaceous species in this study is clear evidence that plant–plant facilitation positively affects the environmental remediation of soils contaminated by trace metals and provides additional information on biodiversity conservation.

4.3. Implications for the Remediation of Soil Polluted by Trace Metals

The results obtained in this study highlight several major implications for the ecological management of contaminated soils and phytoremediation strategies in the Katangan Copper Arc. On the one hand, the observed effectiveness of certain woody species, notably L. leucocephala, A. lebbeck, S. guineense, and A. auriculiformis, demonstrates their potential for revegetation or ecological restoration programs in the context of severe metal pollution [40,42]. Their strong resilience, combined with their sustained growth in amended soils, confirms the relevance of their selection for environmental rehabilitation projects [40,53]. Furthermore, the progressive enrichment in trace metals observed in amended soils reveals the importance of long-term monitoring to prevent soil saturation and guarantee the sustainability of Phyto technological interventions. The maintenance of pH neutrality in amended soils, despite the accumulation of metals, testifies to the crucial role of organic amendments, which promote the chemical stability of the soil and the controlled availability of nutrients required by plants [95,96]. The observations made in this study highlight the need to favor amendments rich in organic matter to limit the mobility and bioavailability of metals and promote beneficial biological activity in the rhizosphere. The fine-tuning of amendment techniques according to local soil properties and environmental conditions is therefore essential to maximize the effectiveness of phytoremediation. Finally, the adoption of combined strategies, such as the introduction of symbiotic micro-organisms (mycorrhizae, growth-promoting bacteria), could strengthen the resilience of plantations to metal pollution. Taken together, these results open up promising prospects for the large-scale application of phytotechnologies in affected mining areas, helping to restore ecosystems and improve the environmental and health conditions of local populations.
In order to critically assess the scope and generalizability of these findings, it is also important to consider the limitations inherent to the present study: (i) soil-focused scope: the research was limited to assessing mineral dynamics in amended soils, without evaluating metal uptake in plant aerial parts or impacts on soil fauna [97,98]; (ii) lack of hydrological monitoring: potential leaching of metals into groundwater was not assessed due to the absence of appropriate tools such as lysimeters or piezometers; (iii) limited sampling frequency: although the study spanned four years, soil sampling was performed at spaced intervals, restricting detailed temporal analysis [99]; (iv) biological indicators not included: key indicators such as microbial activity and soil biodiversity were not considered, despite their importance in ecological assessment [100]; and (v) site-specific context: the results are specific to the Katangan Copperbelt and may not be directly transferable to other pedoclimatic contexts [101]. These limitations guide our future research, which will incorporate plant biomass monitoring, soil biological indicators, and hydrological assessments to provide a more comprehensive evaluation of restoration outcomes.

5. Conclusions

This study examined changes in the mineral composition of soil and woody and herbaceous vegetation at metal-contaminated sites, using in situ experiments. The results show a change in the mineral composition of the soil, with an increase in trace metal concentrations and a decrease in nutrients over a short period. Vegetation dynamics revealed significant differences between individuals planted in amended and unamended pits, with a zero percent survival rate in the latter. The growth in height and circumference of the planted species is notable, reaching up to 8 m in height on average for L. leucocephala and 22 cm in circumference for S. guineense. In addition, 13 spontaneous herbaceous species were observed between the planting corridors of the tree species. These results show that it is possible to revegetate urban soils polluted by trace metals with fast-growing tree species and contribute to the conservation of biodiversity. To help increase the production of ecosystem services through this remediation strategy for soils polluted with trace metals, native woody species should be integrated. Building on this approach and considering the insights gained from our study, it is essential to derive broader lessons that can inform restoration practices beyond the Katanga Copperbelt. Based on the results obtained in the specific context of the Katanga Copperbelt, we suggest that future restoration initiatives in other regions consider the following: (i) the use of site-appropriate organic and mineral amendments that contribute to a successful establishment of tree species in elevated metal-contaminated soil and provide q list of indigenous and exotic species to be used for phytostabilization in tropical areas; (ii) the expansion of environmental monitoring to include groundwater, vegetation, and soil biology for an integrated assessment; (iii) the promotion of sustainable practices relying on local resources to reduce costs and support a circular economy approach; and (iv) the active involvement and capacity building of local stakeholders to ensure the sustainability of interventions. These recommendations aim to broaden the applicability of our findings while respecting regional specificities.

Author Contributions

Conceptualization, S.L., G.C. and M.N.S. methodology, S.L., J.K.M., M.N.S. and G.C.; software, S.L., D.-d.N.N. and J.K.M.; validation, S.L., J.K.M. and M.N.S.; formal analysis, S.L., D.-d.N.N., M.N.S. and G.C.; investigation, S.L., D.-d.N.N. and J.K.M.; resources, G.C. and M.N.S.; data curation, S.L. and M.N.S.; writing—original draft preparation, S.L.; writing—review and editing, G.C. and M.N.S.; visualization, G.C. and M.N.S.; supervision, G.C. and M.N.S.; project administration, G.C.; funding acquisition, G.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

No new data were created or analyzed in this study. Data sharing does not apply to this article.

Acknowledgments

The authors are grateful to the Academy of Research and Higher Education (ARES) through the Zorglub Project for the financial means made available. Serge L. is a research fellow in the Zorglub project. We would like to thank Master Franc Mpetemba wa Kalala for his availability during the implementation of the experiment and Gécamines for providing the space.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Alvarenga, P.; Gonçalves, A.P.; Fernandes, R.M.; De Varennes, A.; Vallini, G.; Duarte, E.; Cunha-Queda, A.C. Organic residues as immobilizing agents in aided phytostabilization: (I) Effects on soil chemical characteristics. Chemosphere 2009, 74, 1292–1300. [Google Scholar] [CrossRef] [PubMed]
  2. Entwistle, J.A.; Hursthouse, A.S.; Marinho Reis, P.A.; Stewart, A.G. Metalliferous Mine Dust: Human Health Impacts and the Potential Determinants of Disease in Mining Communities. Curr. Pollut. Rep. 2019, 5, 67–83. [Google Scholar] [CrossRef]
  3. Doumett, S.; Lamperi, L.; Checchini, L.; Azzarello, E.; Mugnai, S.; Mancuso, S.; Petruzzelli, G.; Del Bubba, M. Heavy metal distribution between contaminated soil and Paulownia tomentosa, in a pilot-scale assisted phytoremediation study: Influence of different complexing agents. Chemosphere 2008, 72, 1481–1490. [Google Scholar] [CrossRef]
  4. Zhuang, P.; McBride, M.B.; Xia, H.; Li, N.; Li, Z. Health risk from heavy metals via consumption of food crops in the vicinity of Dabaoshan mine, South China. Sci. Total Environ. 2009, 407, 1551–1561. [Google Scholar] [CrossRef]
  5. Squadrone, S.; Burioli, E.; Monaco, G.; Koya, M.K.; Prearo, M.; Gennero, S.; Dominici, A.; Abete, M.C. Human exposure to metals due to consumption of fish from an artificial lake basin close to an active mining area in Katanga (D.R. Congo). Sci. Total Environ. 2016, 568, 679–684. [Google Scholar] [CrossRef]
  6. Van Brusselen, D.; Kayembe-Kitenge, T.; Mbuyi-Musanzayi, S.; Lubala Kasole, T.; Kabamba Ngombe, L.; Musa Obadia, P.; Kyanika wa Mukoma, D.; Van Herck, K.; Avonts, D.; Devriendt, K.; et al. Metal mining and birth defects: A case-control study in Lubumbashi, Democratic Republic of the Congo. Lancet Planet Health 2020, 4, e158–e167. [Google Scholar] [CrossRef]
  7. Kabata-Pendias, A.; Mukherjee, A.B. Trace Elements of Group 12 (Previously Group IIb). In Trace Elements from Soil to Human; Springer: Berlin/Heidelberg, Germany, 2007; pp. 283–319. [Google Scholar] [CrossRef]
  8. Duvigneaud, P.; Denaeyer-De Smet, S. Cuivre et végétation au Katanga. Bull. Société R. Bot. Belg. 1963, 96, 93–231. [Google Scholar]
  9. Faucon, M.-P.; Colinet, G.; Mahy, G.; Ngongo Luhembwe, M.; Verbruggen, N.; Meerts, P. Soil influence on Cu and Co uptake and plant size in the cuprophytes Crepidorhopalon perennis and C. tenuis (Scrophulariaceae) in SC Africa. Plant Soil 2009, 317, 201–212. [Google Scholar] [CrossRef]
  10. Leblanc, M.; Malaisse, F. Lubumbashi, un Écosystème Urbain Tropical; Centre International de Sémiologie, Université Nationale du Zaïre: Lubumbashi, République du Zaïre, 1978; pp. 95–96. [Google Scholar]
  11. Vangronsveld, J.; Herzig, R.; Weyens, N.; Boulet, J.; Adriaensen, K.; Ruttens, A.; Thewys, T.; Vassilev, A.; Meers, E.; Nehnevajova, E.; et al. Phytoremediation of contaminated soils and groundwater: Lessons from the field. Environ. Sci. Pollut. Res. 2009, 16, 765–794. [Google Scholar] [CrossRef]
  12. Narendrula, R.; Nkongolo, K.K.; Beckett, P. Comparative Soil Metal Analyses in Sudbury (Ontario, Canada) and Lubumbashi (Katanga, DR-Congo). Bull. Environ. Contam. Toxicol. 2012, 88, 187–192. [Google Scholar] [CrossRef]
  13. Pourret, O.; Lange, B.; Bonhoure, J.; Colinet, G.; Decrée, S.; Mahy, G.; Séleck, M.; Shutcha, M.; Faucon, M.-P. Assessment of soil metal distribution and environmental impact of mining in Katanga (Democratic Republic of Congo). Appl. Geochem. 2016, 64, 43–55. [Google Scholar] [CrossRef]
  14. Mpinda, M.T.; Mujinya, B.B.; Mees, F.; Kasangij, P.K.; Van Ranst, E. Patterns and forms of copper and cobalt in Macrotermes falciger mounds of the Lubumbashi area, DR Congo. J. Geochem. Explor. 2022, 238, 107002. [Google Scholar] [CrossRef]
  15. Atibu, E.K.; Devarajan, N.; Thevenon, F.; Mwanamoki, P.M.; Tshibanda, J.B.; Mpiana, P.T.; Prabakar, K.; Mubedi, J.I.; Wildi, W.; Poté, J. Concentration of metals in surface water and sediment of Luilu and Musonoie Rivers, Kolwezi-Katanga, Democratic Republic of Congo. Appl. Geochem. 2013, 39, 26–32. [Google Scholar] [CrossRef]
  16. Mudimbi, K.D.; Kabamba, T.A.; Kodondi, K.F.; Luboya, N.O.; Kasongo, B.C.; Kabundi, K.D.; Kisunka, B.Y.; Musola, C.H.; Longanga, O.A.; Lukumwena, K.Z. Impact of mining on water of the rivers Shinkolobwe, Lwisha and Kansonga in the province of Katanga (DRC). J. Med. Res. 2017, 3, 71–73. [Google Scholar]
  17. Banza, C.L.N.; Nawrot, T.S.; Haufroid, V.; Decrée, S.; De Putter, T.; Smolders, E.; Kabyla, B.I.; Luboya, O.N.; Ilunga, A.N.; Mutombo, A.M.; et al. High human exposure to cobalt and other metals in Katanga, a mining area of the Democratic Republic of Congo. Environ. Res. 2009, 109, 745–752. [Google Scholar] [CrossRef]
  18. Cheyns, K.; Banza Lubaba Nkulu, C.; Ngombe, L.K.; Asosa, J.N.; Haufroid, V.; De Putter, T.; Nawrot, T.; Kimpanga, C.M.; Numbi, O.L.; Ilunga, B.K.; et al. Pathways of human exposure to cobalt in Katanga a mining area of the D.R. Congo. Sci. Total Environ. 2014, 490, 313–321. [Google Scholar] [CrossRef]
  19. Mukendi, R.-A.-M.; Banza, C.L.N.; Mukeng, C.-A.-K.; Ngwe, J.T.M.; Mwembo, A.N.-A.-N.; Kalenga, P.M.K. Human exposure to metallic traced elements and sperm alteration: A study conducted in the mining areas of Haut-Katanga in the Democratic Republic of Congo. Pan Afr. Med. J. 2018, 30, 35. [Google Scholar] [CrossRef]
  20. Gerwing, T.G.; Hawkes, V.C.; Gann, G.D.; Murphy, S.D. Restoration, reclamation, and rehabilitation: On the need for, and positing a definition of, ecological reclamation. Restor. Ecol. 2022, 30, e13461. [Google Scholar] [CrossRef]
  21. Sun, W.; Ji, B.; Khoso, S.A.; Tang, H.; Liu, R.; Wang, L.; Hu, Y. An extensive review on restoration technologies for mining tailings. Environ. Sci. Pollut. Res. 2018, 25, 33911–33925. [Google Scholar] [CrossRef]
  22. Awa, S.H.; Hadibarata, T. Removal of Heavy Metals in Contaminated Soil by Phytoremediation Mechanism: A Review. Water Air Soil Pollut. 2020, 231, 47. [Google Scholar] [CrossRef]
  23. Huslina, F.; Khudur, L.S.; Shah, K.; Surapaneni, A.; Netherway, P.; Ball, A.S. Mine Site Restoration: The Phytoremediation of Arsenic-Contaminated Soils. Environments 2024, 11, 99. [Google Scholar] [CrossRef]
  24. Pinho, R.C.; Miller, R.P.; Alfaia, S.S. Agroforestry and the Improvement of Soil Fertility: A View from Amazonia. Appl. Environ. Soil Sci. 2012, 2012, 616383. [Google Scholar] [CrossRef]
  25. Fahad, S.; Chavan, S.B.; Chichaghare, A.R.; Uthappa, A.R.; Kumar, M.; Kakade, V.; Pradhan, A.; Jinger, D.; Rawale, G.; Yadav, D.K.; et al. Agroforestry Systems for Soil Health Improvement and Maintenance. Sustainability 2022, 14, 14877. [Google Scholar] [CrossRef]
  26. Podar, D.; Maathuis, F.J.M. The role of roots and rhizosphere in providing tolerance to toxic metals and metalloids. Plant Cell Environ. 2022, 45, 719–736. [Google Scholar] [CrossRef]
  27. Bedair, H.; Ghosh, S.; Abdelsalam, I.M.; Keerio, A.A.; AlKafaas, S.S. Potential implementation of trees to remediate contaminated soil in Egypt. Environ. Sci. Pollut. Res. 2022, 29, 78132–78151. [Google Scholar] [CrossRef]
  28. Kidd, P.; Barceló, J.; Bernal, M.P.; Navari-Izzo, F.; Poschenrieder, C.; Shilev, S.; Clemente, R.; Monterroso, C. Trace element behaviour at the root–soil interface: Implications in phytoremediation. Environ. Exp. Bot. 2009, 67, 243–259. [Google Scholar] [CrossRef]
  29. Munyemba, K.; Bamba, I.; Djibu, K.J.P.; Amisi, M.; Veroustraete, F.; Ngongo, L.M.; Bogaert, J. Occupation des sols Dans le Cône de Pollution à Lubumbashi; Presses Universitaires de Lubumbashi: Lubumbashi, Democratic Republic of the Congo, 2008; Volume 1, pp. 19–22. [Google Scholar]
  30. Mpundu, M.M.; Useni, S.Y.; Nyembo, K.L.; Colinet, G. Effets d’amendements carbonatés et organiques sur la culture de deux légumes sur sol contaminé à Lubumbashi (RD Congo). BASE 2014, 18, 367–375. [Google Scholar]
  31. Mwanasomwe, K.J. Amélioration du Procédé de Phytostabilisation Avec les Espèces Ligneuses Pour la Production des Services Écosystémiques en Milieux Pollués Urbains et Périurbains de L’arc Cuprifère Katangais. Ph.D. Thesis, Université de Liège Gembloux-Agro Bio Tech, Gembloux, Belgium, 2022. [Google Scholar]
  32. Langunu, S.; Imabo, P.M.I.; Bibi Fwanda, B.; Kilela Mwanasomwe, J.; Colinet, G.; Ngoy Shutcha, M. Accumulation of Trace Metals in Fruits from Mango and Syzygium guineense Growing in Residential Households from a Contaminated District of Lubumbashi (DR Congo): Is Fruit Consumption at Risk? Toxics 2023, 11, 620. [Google Scholar] [CrossRef]
  33. Mwanasomwe, J.K.; Langunu, S.; Shutcha, M.N.; Colinet, G. Effects of 15-Year-Old Plantation on Soil Conditions, Spontaneous Vegetation, and the Trace Metal Content in Wood Products at Kipushi Tailings Dam. Front. Soil Sci. 2022, 2, 934491. [Google Scholar] [CrossRef]
  34. Drew, D.M.; Downes, G.M. The use of precision dendrometers in research on daily stem size and wood property variation: A review. Dendrochronologia 2009, 27, 159–172. [Google Scholar] [CrossRef]
  35. Duchesne, L.; Houle, D. Modelling day-to-day stem diameter variation and annual growth of balsam fir (Abies balsamea (L.) Mill.) from daily climate. For. Ecol. Manag. 2011, 262, 863–872. [Google Scholar] [CrossRef]
  36. Ngongo, M.L.; Van Ranst, E.; Baert, G.; Kasongo, E.L.; Verdoodt, A.; Mujinya, B.B.; Mukalay, J.M.; Guide des Sols en, R.D. Etude et Gestion; Congo Tome I; UGent, UNILU: Lubumbashi, Democratic Republic of the Congo, 2009; p. 262. [Google Scholar]
  37. Shutcha, M.N.; Mukobo, R.P.; Muyumba, K.D.; Mpundu, M.M.; Faucon, M.P.; Lubalega, K.T.; Ludovic, A.; Annabelle, J.; Vandenheede, N.; Pourret, O.; et al. Pedogeochemical background and mapping of soil pollution in Lubumbashi. In Anthropisation des paysages Katangais; Bogaert, J., Gilles, C., Gregory, M., Eds.; Les Presses Agronomiques de Gembloux: Gembloux, Belgium, 2018; pp. 215–228. [Google Scholar]
  38. Malaisse, F. How to Live and Survive in Zambezian Open Forest (Miombo Ecoregion); Presses Agronomiques de Gembloux: Gembloux, Belgium, 2010. [Google Scholar]
  39. Kalombo, K.D. Caractérisation de la répartition temporelle des précipitations à Lubumbashi (Sud-Est de la RDC) sur la période 1970–2014. In Proceedings of the XXIII Colloque de l’Association Internationale de Climatologie, Liège, Belgium, 12–13 July 2015; pp. 531–536. [Google Scholar]
  40. Meeinkuirt, W.; Pokethitiyook, P.; Kruatrachue, M.; Tanhan, P.; Chaiyarat, R. Phytostabilization of a pb-contaminated mine tailing by various tree species in pot and field trial experiments. Int. J. Phytoremediat. 2012, 14, 925–938. [Google Scholar] [CrossRef] [PubMed]
  41. Kambing’a, M.K.; Syampungani, S. Performance des espèces d’arbres poussant sur les sols des barrages de résidus en Zambie: Une base pour la sélection des espèces pour la revégétalisation des barrages de résidus. J. Environ. Sci. Eng. 2012, 1, 827. [Google Scholar]
  42. Mpundu, M.M.; Amandine, L.; Shutcha, N.M.; Michel, N.L.; Gilles, C. Phytostabilisation des sols contaminés au Katanga: Résultats d’expérimentations sur la sélection d’espèces ligneuses combinée à des doses croissantes d’amendements. In Anthropisation des Paysages Katangais; Bogaert, J., Gilles, C., Gregory, M., Eds.; Les Presses Agronomiques de Gembloux: Gembloux, Belgium, 2018; pp. 177–191. [Google Scholar]
  43. Mwanasomwe, J.K.; Langunu, S.; Nkulu, S.N.; Shutcha, M.N.; Colinet, G. Effect of Organic Amendment on the Physicochemical Characteristics of Tailings Dam Soil and Root Development of Tree Species, Fifteen Years After Planting. Front. Soil Sci. 2022, 2, 934999. [Google Scholar] [CrossRef]
  44. Meerts, P. An annotated checklist to the trees and shrubs of the Upper Katanga (D. R. Congo). Phytotaxa 2016, 258, 201–250. [Google Scholar] [CrossRef]
  45. Useni, Y.S.; Malaisse, F.; Yona, J.M.; Mwamba, T.M.; Bogaert, J. Diversity, use and management of household-located fruit trees in two rapidly developing towns in Southeastern D.R. Congo. Urban For. Urban Green. 2021, 63, 127220. [Google Scholar] [CrossRef]
  46. Mwanasomwe, J.K. Sélection des Espèces Ligneuses Pour la Phytostabilisation et la Valorisation des Sols Contaminés en ETMs de Gécamines/Penga Penga. Master’s Thesis, Université de Lubumbashi, Lubumbashi, République Démocratique du Congo, 2012; p. 56. [Google Scholar]
  47. Rondeux, J. La Mesure des Arbres et des Peuplements Forestiers, 3rd ed.; Les Presses Universitaires de Liège, Les Presses Agronomiques de Gembloux: Gembloux, Belgium, 2021; 738p, Available online: http://hdl.handle.net/2268/262622 (accessed on 20 February 2025).
  48. Ameja, L.G.; Ribeiro, N.; Sitoe, A.A.; Guillot, B. Regeneration and Restoration Status of Miombo Woodland Following Land Use Land Cover Changes at the Buffer Zone of Gile National Park, Central Mozambique. Trees For. People 2022, 9, 100290. [Google Scholar] [CrossRef]
  49. Furman, B.T.; Leone, E.H.; Bell, S.S.; Durako, M.J.; Hall, M.O. Braun-Blanquet data in ANOVA designs: Comparisons with percent cover and transformations using simulated data. Mar. Ecol. Prog. Ser. 2018, 597, 13–22. [Google Scholar] [CrossRef]
  50. Nsielolo, K.R.; Kiyulu, B.J.; Ndungu, M.R. Inventaire floristique de la forêt sacrée de Wuya dans la province du Kongo-central en République Démocratique du Congo. Afr. Sci. 2020, 16, 218–225. [Google Scholar]
  51. Liénard, A.; Colinet, G. Assessment of vertical contamination of Cd, Pb and Zn in soils around a former ore smelter in Wallonia, Belgium. Environ. Earth Sci. 2016, 75, 1322. [Google Scholar] [CrossRef]
  52. Sastre, J.; Sahuquillo, A.; Vidal, M.; Rauret, G. Determination of Cd, Cu, Pb and Zn in environmental samples: Microwave-assisted total digestion versus aqua regia and nitric acid extraction. Anal. Chim. Acta 2002, 1, 59–72. [Google Scholar] [CrossRef]
  53. Gnahoua, G.; Nguessan, K.; Balle, P. Les jachères de légumineuses arborescentes: Sources potentielles de bois énergie et de service en Côte d’Ivoire. J. Appl. Biosci. 2014, 1, 7290. [Google Scholar] [CrossRef]
  54. Shutcha, M.N.; Faucon, M.-P.; Kamengwa Kissi, C.; Colinet, G.; Mahy, G.; Ngongo Luhembwe, M.; Visser, M.; Meerts, P. Three years of phytostabilisation experiment of bare acidic soil extremely contaminated by copper smelting using plant biodiversity of metal-rich soils in tropical Africa (Katanga, DR Congo). Ecol. Eng. 2015, 82, 81–90. [Google Scholar] [CrossRef]
  55. Mpinda, M.T.; Kisimba, T.N.; Mwamba, T.M.; Kasongo, E.L.M.; Kaniki, A.T.; Mujinya, B.B. Baseline Concentrations of 11 Elements as a Function of Land uses in Surface Soils of the Katangese Copperbelt Area (D.R. Congo). Am. J. Environ. Sci. 2021, 17, 125–135. [Google Scholar] [CrossRef]
  56. de Oliveira, V.P.; Martins, W.B.R.; Rodrigues, J.I.d.M.; Silva, A.R.; Lopes, J.D.C.A.; Neto, J.F.d.L.; Schwartz, G. Are liming and pit size determining for tree species establishment in degraded areas by kaolin mining? Ecol. Eng. 2022, 178, 106599. [Google Scholar] [CrossRef]
  57. Yang, Y.; Dong, M.; Cao, Y.; Wang, J.; Tang, M.; Ban, Y. Comparisons of Soil Properties, Enzyme Activities and Microbial Communities in Heavy Metal Contaminated Bulk and Rhizosphere Soils of Robinia pseudoacacia L. in the Northern Foot of Qinling Mountain. Forests 2017, 8, 430. [Google Scholar] [CrossRef]
  58. Ayari, F.; Hamdi, H.; Jedidi, N.; Gharbi, N.; Kossai, R. Heavy metal distribution in soil and plant in municipal solid waste compost amended plots. Int. J. Environ. Sci. Technol. 2010, 7, 465–472. [Google Scholar] [CrossRef]
  59. Abd-Elhalim, B.T.; Gideon, M.; Anton, K.; Boyi, M.O. Impact of Dumpsite-Derived Compost on Heavy Metal Accumulation in Cultivated Maize and Spinach. BMC Res. Notes 2025, 18, 20. [Google Scholar] [CrossRef] [PubMed]
  60. Huang, B.; Yuan, Z.; Li, D.; Zheng, M.; Nie, X.; Liao, Y. Effects of soil particle size on the adsorption, distribution, and migration behaviors of heavy metal(loid)s in soil: A review. Environ. Sci. Process. Impacts 2020, 22, 1596–1615. [Google Scholar] [CrossRef]
  61. Langunu, S. Evaluation de L’efficacité de la Phytoremédiation de sols Pollués en Métaux Traces dans L’arc Cuprifère Katangais (République Démocratique du Congo). Ph.D. Thesis, Université de Liège—Gembloux Agro-Bio Tech, Gembloux, Belgium, 2025; 271p. [Google Scholar]
  62. Legrand, P.; Turmel, M.-C.; Sauvé, S.; Courchesne, F. Speciation and bioavailability of trace metals (Cd, Cu, Ni, Pb, Zn) in the rhizosphere of contaminated soils. In Biogeochemistry of Trace Elements in the Rhizosphere; Elsevier: Amsterdam, The Netherlands, 2005; pp. 261–299. [Google Scholar] [CrossRef]
  63. Kafle, A.; Timilsina, A.; Gautam, A.; Adhikari, K.; Bhattarai, A.; Aryal, N. Phytoremediation: Mechanisms, plant selection and enhancement by natural and synthetic agents. Environ. Adv. 2022, 8, 100203. [Google Scholar] [CrossRef]
  64. Aryal, M. Phytoremediation strategies for mitigating environmental toxicants. Heliyon 2024, 10, e38683. [Google Scholar] [CrossRef] [PubMed]
  65. Wu, Q.; Wang, S.; Thangavel, P.; Li, Q.; Zheng, H.; Bai, J.; Qiu, R. Phytostabilization potential of Jatropha curcas L. in polymetallic acid mine tailings. Int. J. Phytoremediat. 2011, 13, 788–804. [Google Scholar] [CrossRef]
  66. Olaniran, A.; Balgobind, A.; Pillay, B. Bioavailability of Heavy Metals in Soil: Impact on Microbial Biodegradation of Organic Compounds and Possible Improvement Strategies. Int. J. Mol. Sci. 2013, 14, 10197–10228. [Google Scholar] [CrossRef] [PubMed]
  67. Colombo, C.; Palumbo, G.; He, J.-Z.; Pinton, R.; Cesco, S. Review on iron availability in soil: Interaction of Fe minerals, plants, and microbes. J. Soils Sediments 2014, 14, 538–548. [Google Scholar] [CrossRef]
  68. Antoniadis, V.; Levizou, E.; Shaheen, S.M.; Ok, Y.S.; Sebastian, A.; Baum, C.; Prasad, M.N.V.; Wenzel, W.W.; Rinklebe, J. Trace elements in the soil-plant interface: Phytoavailability, translocation, and phytoremediation—A review. Earth-Sci. Rev. 2017, 171, 621–645. [Google Scholar] [CrossRef]
  69. Madejón, P.; Marañón, T.; Navarro-Fernández, C.M.; Domínguez, M.T.; Alegre, J.M.; Robinson, B.; Murillo, J.M.; Paz-Ferreiro, J. Potential of Eucalyptus camaldulensis for phytostabilization and biomonitoring of trace-element contaminated soils. PLoS ONE 2017, 12, e0180240. [Google Scholar] [CrossRef] [PubMed]
  70. Barrow, N.J.; Hartemink, A.E. The effects of pH on nutrient availability depend on both soils and plants. Plant Soil 2023, 487, 21–37. [Google Scholar] [CrossRef]
  71. Palansooriya, K.N.; Shaheen, S.M.; Chen, S.S.; Tsang, D.C.W.; Hashimoto, Y.; Hou, D.; Bolan, N.S.; Rinklebe, J.; Ok, Y.S. Soil amendments for immobilization of potentially toxic elements in contaminated soils: A critical review. Environ. Int. 2020, 134, 105046. [Google Scholar] [CrossRef]
  72. Hnini, M.; Rabeh, K.; Oubohssaine, M. Interactions between beneficial soil microorganisms (PGPR and AMF) and host plants for environmental restoration: A systematic review. Plant Stress 2024, 11, 100391. [Google Scholar] [CrossRef]
  73. Paniagua-López, M.; Silva-Castro, G.A.; Romero-Freire, A.; Martín-Peinado, F.J.; Sierra-Aragón, M.; García-Romera, I. Integrating waste valorization and symbiotic microorganisms for sustainable bioremediation of metal(loid)-polluted soils. Sci. Total Environ. 2024, 945, 174030. [Google Scholar] [CrossRef]
  74. ADEME. Phytotechnologies appliquées aux sites pollués. In Proceedings of the Journée Technique Nationale, Recueil des Interventions, Paris, France, 17 October 2012; p. 115. [Google Scholar]
  75. Lee, S.-H.; Ji, W.; Lee, W.-S.; Koo, N.; Koh, I.H.; Kim, M.-S.; Park, J.-S. Influence of amendments and aided phytostabilization on metal availability and mobility in Pb/Zn mine tailings. J. Environ. Manag. 2014, 139, 15–21. [Google Scholar] [CrossRef]
  76. Labidi, S.; Firmin, S.; Verdin, A.; Bidar, G.; Laruelle, F.; Douay, F.; Shirali, P.; Fontaine, J.; Lounès-Hadj Sahraoui, A. Nature of fly ash amendments differently influences oxidative stress alleviation in four forest tree species and metal trace element phytostabilization in aged contaminated soil: A long-term field experiment. Ecotoxicol. Environ. Saf. 2017, 138, 190–198. [Google Scholar] [CrossRef] [PubMed]
  77. Khan, A.G. Role of soil microbes in the rhizospheres of plants growing on trace metal contaminated soils in phytoremediation. J. Trace Elem. Med. Biol. 2005, 18, 355–364. [Google Scholar] [CrossRef] [PubMed]
  78. Wenzel, W.W. Rhizosphere processes and management in plant-assisted bioremediation (phytoremediation) of soils. Plant Soil 2009, 321, 385–408. [Google Scholar] [CrossRef]
  79. Gupta, N.; Fischer, A.R.H.; Frewer, L.J. Socio-psychological determinants of public acceptance of technologies: A review. Public Underst. Sci. 2012, 21, 782–795. [Google Scholar] [CrossRef]
  80. Bolia, N.E.; Bosanza, J.B.Z.; Mongeke, M.M.; Ngbolua, K.T.N. Études Dendrométrique et Floristique des Forêts à Gilbertiodendron Dewevrei d’une Concession Forestière en République Démocratique du Congo. 2019. Available online: https://www.agrimaroc.org/index.php/Actes_IAVH2/article/view/677#google_vignette (accessed on 20 February 2025).
  81. Ewango, C.; Maindo, A.; Shaumba, J.P.; Kyanga, M.; Macqueen, D. Options for Sustainable Community Forestry Business Incubation in the Democratic Republic of Congo (DRC); IIED: London, UK, 2019; Available online: https://www.iied.org/13613iied (accessed on 20 February 2025).
  82. Bisiaux, F.; Peltier, R.; Muliele, J.C. Plantations industrielles et agroforesterie au service des populations des plateaux Batéké, Mampu, en République démocratique du Congo. Bois For. Des. Trop. 2009, 301, 21–32. [Google Scholar] [CrossRef]
  83. Proces, P.; Dubiez, E.; Bisiaux, F.; Péroches, A.; Fayolle, A. Production d’Acacia auriculiformis dans le système agroforestier de Mampu, plateau Batéké, République démocratique du Congo. Bois For. Des. Trop. 2018, 334, 23. [Google Scholar] [CrossRef]
  84. Kaboneka, S.; Ndayishimiye, J.; Nkurunziza, C.; Ndorere, V.; Nyengayenge, D.; Ndayisaba, D. Adaptation et croissance des acacias australiens introduits au Burundi. Rev. L’université Burundi (Sci. Exactes Nat.) 2020, 29, 45–55. [Google Scholar]
  85. Wang, F.; Li, Z.; Xia, H.; Zou, B.; Li, N.; Liu, J.; Zhu, W. Effects of nitrogen-fixing and non-nitrogen-fixing tree species on soil properties and nitrogen transformation during forest restoration in southern China. Soil Sci. Plant Nutr. 2010, 56, 297–306. [Google Scholar] [CrossRef]
  86. Sarwar, N.; Imran, M.; Shaheen, M.R.; Ishaque, W.; Kamran, M.A.; Matloob, A.; Rehim, A.; Hussain, S. Phytoremediation strategies for soils contaminated with heavy metals: Modifications and future perspectives. Chemosphere 2017, 171, 710–721. [Google Scholar] [CrossRef]
  87. Albert, K.M. Role of revegetation in restoring fertility of degraded mined soils in Ghana: A review. Int. J. Biodivers. Conserv. 2015, 7, 57–80. [Google Scholar] [CrossRef]
  88. Antwi-Boasiako, A.; Amponsah, P.; Adoma Opoku, J.; Coulibaly, D.; Mintah, P. Increasing Mango Production Efficiency under the Fast-Changing Climate. In Abiotic Stress in Crop Plants—Ecophysiological Responses and Molecular Approaches; Hasanuzzaman, M., Nahar, K., Eds.; IntechOpen: London, UK, 2024. [Google Scholar] [CrossRef]
  89. Vospernik, S.; Heym, M.; Pretzsch, H.; Pach, M.; Steckel, M.; Aldea, J.; Brazaitis, G.; Bravo-Oviedo, A.; Del Rio, M.; Löf, M.; et al. Tree species growth response to climate in mixtures of Quercus robur/Quercus petraea and Pinus sylvestris across Europe—A dynamic, sensitive equilibrium. For. Ecol. Manag. 2023, 530, 120753. [Google Scholar] [CrossRef]
  90. Conesa, H.M.; Faz, Á. Metal Uptake by Spontaneous Vegetation in Acidic Mine Tailings from a Semiarid Area in South Spain: Implications for Revegetation and Land Management. Water Air Soil Pollut. 2011, 215, 221–227. [Google Scholar] [CrossRef]
  91. Schleicher, J.; Meyer, K.M.; Wiegand, K.; Schurr, F.M.; Ward, D. Disentangling facilitation and seed dispersal from environmental heterogeneity as mechanisms generating associations between savanna plants: Cause of spatial associations of savanna plant species. J. Veg. Sci. 2011, 22, 1038–1048. [Google Scholar] [CrossRef]
  92. Cheng, X.-L.; Padullés Cubino, J.; Balfour, K.; Zhu, Z.-X.; Wang, H.-F. Drivers of spontaneous and cultivated species diversity in the tropical city of Zhanjiang, China. Urban For. Urban Green. 2022, 67, 127428. [Google Scholar] [CrossRef]
  93. Chen, F.; Yang, Y.; Mi, J.; Liu, R.; Hou, H.; Zhang, S. Effects of Vegetation Pattern and Spontaneous Succession on Remediation of Potential Toxic Metal-Polluted Soil in Mine Dumps. Sustainability 2019, 11, 397. [Google Scholar] [CrossRef]
  94. Boisson, S.; Collignon, J.; Langunu, S.; Lebrun, J.; Shutcha, M.N.; Mahy, G. Reconciling phytostabilisation of polluted soils with conservation of cupro-cobaltic flora with a novel strategy to enhance extreme ecosystems? In Territoires Périurbains. Développement, Enjeux et Perspectives dans les Pays du Sud; Bogaert, J., Halleux, J.-M., Eds.; Les Presses Agronomiques de Gembloux: Gembloux, Belgium, 2015; pp. 127–138. [Google Scholar]
  95. Bolan, N.; Naidu, R.; Choppala, G.; Park, J.; Mora, M.L.; Budianta, D.; Panneerselvam, P. Solute Interactions in Soils about the Bioavailability and Environmental Remediation of Heavy Metals and Metalloids. Pedologist 2012, 53, 1–18. [Google Scholar]
  96. Kumpiene, J.; Lagerkvist, A.; Maurice, C. Stabilization of As, Cr, Cu, Pb and Zn in soil using amendments—A review. Waste Manag. 2008, 28, 215–225. [Google Scholar] [CrossRef]
  97. Kabata-Pendias, A.; Szteke, B. Trace Elements in Abiotic and Biotic Environments, 1st ed.; CRC Press: Boca Raton, FL, USA, 2015. [Google Scholar] [CrossRef]
  98. Senila, M.; Kovacs, E. Use of diffusive gradients in thin-film technique to predict the mobility and transfer of nutrients and toxic elements from agricultural soil to crops—An overview of recent studies. Environ. Sci. Pollut. Res. 2024, 31, 34817–34838. [Google Scholar] [CrossRef]
  99. Lawrence, G.B.; Fernandez, I.J.; Richter, D.D.; Ross, D.S.; Hazlett, P.W.; Bailey, S.W.; Ouimet, R.; Warby, R.A.F.; Johnson, A.H.; Lin, H.; et al. Measuring Environmental Change in Forest Ecosystems by Repeated Soil Sampling: A North American Perspective. J. Environ. Qual. 2013, 42, 623–639. [Google Scholar] [CrossRef]
  100. El-Sharkawy, G.; Alotaibi, M.O.; Zuhair, R.; Mahmoud, E.; El Baroudy, A.; Omara, A.E.-D.; El-Sharkawy, M. Ecological Assessment of Polluted Soils: Linking Ecological Risks, Soil Quality, and Biota Diversity in Contaminated Soils. Sustainability 2025, 17, 1524. [Google Scholar] [CrossRef]
  101. Shutcha, M.N.; Mubemba, M.M.; Faucon, M.-P.; Luhembwe, M.N.; Visser, M.; Colinet, G.; Meerts, P. Phytostabilisation of Copper-Contaminated Soil in Katanga: An Experiment with Three Native Grasses and Two Amendments. Int. J. Phytoremediat. 2010, 12, 616–632. [Google Scholar] [CrossRef] [PubMed]
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Figure 1. Location of the GCM/Penga Penga experimental plot. The red dot indicates the location of the experimental plot and the green dot indicates the mountain of slag from the Gécamines copper smelting industry.
Figure 1. Location of the GCM/Penga Penga experimental plot. The red dot indicates the location of the experimental plot and the green dot indicates the mountain of slag from the Gécamines copper smelting industry.
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Figure 2. Overview of the six-tree species planted in the phytostabilisation experiment. (a) Acacia auriculiformis, (b) Albizia lebbeck, (c) Delonix regia, (d) Leucaena leucocephala, (e) Mangifera indica, and (f) Syzygium guineense. (Photo by Serge Langunu).
Figure 2. Overview of the six-tree species planted in the phytostabilisation experiment. (a) Acacia auriculiformis, (b) Albizia lebbeck, (c) Delonix regia, (d) Leucaena leucocephala, (e) Mangifera indica, and (f) Syzygium guineense. (Photo by Serge Langunu).
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Figure 4. Diameter structure of the woody stand installed at Penga Penga after 50 months of cultivation.
Figure 4. Diameter structure of the woody stand installed at Penga Penga after 50 months of cultivation.
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Figure 5. Overview of tree planting on metal-polluted soil at 4 years of growth. Photo by Serge Langunu, April 2024.
Figure 5. Overview of tree planting on metal-polluted soil at 4 years of growth. Photo by Serge Langunu, April 2024.
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Figure 6. Relationship between tree frequency and diameter at breast height at 50 months for each species grown in trials.
Figure 6. Relationship between tree frequency and diameter at breast height at 50 months for each species grown in trials.
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Figure 7. Flowering of woody species in the 2019–2020 to 2023–2024 cropping seasons.
Figure 7. Flowering of woody species in the 2019–2020 to 2023–2024 cropping seasons.
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Figure 8. Spontaneous colonization and undergrowth regeneration of herbaceous species. Photo by Serge Langunu, April 2024.
Figure 8. Spontaneous colonization and undergrowth regeneration of herbaceous species. Photo by Serge Langunu, April 2024.
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Table 1. List of species tested in the remediation of soils polluted by trace metals. TM: metal tolerance, CR: rapid growth, PBE: high biomass production, SR: deep root system, FC: edible fruit.
Table 1. List of species tested in the remediation of soils polluted by trace metals. TM: metal tolerance, CR: rapid growth, PBE: high biomass production, SR: deep root system, FC: edible fruit.
FamilySpeciesOriginal StatusFunctional Group
FabaceaeAcacia auriculiformis A. Cunn. Ex. BenthExTM/CR/PBE/SR
FabaceaeAlbizia lebbeck (L.) BenthExTM/CR/PBE/SR
FabaceaeDelonix regia (Bojer ex Hook.) Raf.ExTM/PBE/SR
FabaceaeLeucaena. Leucocephala (Lam.) de WitExTM/CR/PBE/SR
Myrtaceae* Syzygium guineense (Willd) DC. Sub macrocarpumInTM/CR/PBE/SR/FC
AnacardiceaeMangifera indica L.ExTM/SR/FC
In: indigenous species; Ex: exotic species. Species marked with * are characteristic of the Miombo forest [44,45].
Table 2. Physicochemical properties of soil from the site and urban waste used (n = 10). Average (minimum–maximum) AsT CdT CoT CuT PbT and ZnT = total concentrations of As, Cd, Co, Cu, Pb, and Zn; CdS, CoS, CuS, PbS, and ZnS = soluble concentrations (extractable with 0.01 M CaCl2).
Table 2. Physicochemical properties of soil from the site and urban waste used (n = 10). Average (minimum–maximum) AsT CdT CoT CuT PbT and ZnT = total concentrations of As, Cd, Co, Cu, Pb, and Zn; CdS, CoS, CuS, PbS, and ZnS = soluble concentrations (extractable with 0.01 M CaCl2).
ParametersTest SoilMunicipal Compost
pHkcl5.5 (4.5–5.6)7.2 (7.2–7.3)
TOC1.9 (0.8–2.6)-
Fe (%)-5.4 (4.7–6.2)
P (mg kg−1)5,3 (2.8–8.9)1327 (413.3–1898)
K (mg kg−1)1.0 (0.7–1.3)3133 (2995.2–3238)
Ca (mg kg−1)9.5 (3.6–20.6)21,797 (6153–30,348)
Mg (mg kg−1)1.4 (1.1–2.0)2791 (1542–3457)
As(T) (mg kg−1)232.1 (254.7–396.6)16.2 (14.1–17.2)
Cd(T) (mg kg−1)33 (23.5–52.3)2.7 (4.3–1.4)
Cu(T) (mg kg−1)17,330 (1462–29,216)725 (707–896)
Co(T) (mg kg−1)295 (276–505)151 (149–187)
Pb(T) (mg kg−1)1168 (1213–1723)62 (35–104)
Zn(T) (mg kg−1)3189.7 (2878–5347)558 (173–1114)
Cd(s) (mg kg−1)2.8 (1.5–4.5)0.01 (0.008–0.035)
Cu(s) (mg kg−1)104.9 (39.2–199.6)0.709 (0.177–1.631)
Co(s) (mg kg−1)19.8 (13.3–29.3)0.089 (0.007–0.263)
Pb(s) (mg kg−1)3.05 (0.7–7.3)0.128 (0.105–0.152)
Zn(s) (mg kg−1)152.7 (124.7–195.3)0.470 (0.033–1.277)
Table 3. Changes in pH values and total levels of major elements (P, K, Ca, and Mg) in the soil from 2019 to 2023. The trial was installed at Gécamines/Penga Penga (n = 10). The mean ± standard deviation represents values; sampling depth = 0–30 cm; n represents the number of samples.
Table 3. Changes in pH values and total levels of major elements (P, K, Ca, and Mg) in the soil from 2019 to 2023. The trial was installed at Gécamines/Penga Penga (n = 10). The mean ± standard deviation represents values; sampling depth = 0–30 cm; n represents the number of samples.
Parameters20192023
PHKCl7.2 ± 0.037.2 ± 0.2
Al (%)3.1 ± 0.323.8 ± 0.31
Fe (%)5.4 ± 0.615.0 ± 0.63
P (mg kg−1)1.327 ± 688516 ± 71.0
K (mg kg−1)3133 ± 101.82497 ± 182.6
Ca (mg kg−1)21.797 ± 10.86212.262 ± 6.062
Mg (mg kg−1)2.791 ± 8713.550 ± 695
Table 4. Trends in trace metal concentrations in soil from 2019 to 2023. The test was installed at Gécamines/Penga Penga (n = 10). The mean ± standard deviation represents the values; sampling depth = 0–30 cm; n represents the number of samples.
Table 4. Trends in trace metal concentrations in soil from 2019 to 2023. The test was installed at Gécamines/Penga Penga (n = 10). The mean ± standard deviation represents the values; sampling depth = 0–30 cm; n represents the number of samples.
Metals20192023
As (mg kg−1)16.2 ± 1.495 ± 28.5
Cd (mg kg−1)2.7 ± 1.38.7 ± 2.0
Cu (mg kg−1)725 ± 1366.141 ± 1.853
Co (mg kg−1)151 ± 36.3182 ± 113
Pb (mg kg−1)62 ± 32421 ± 160
Zn (mg kg−1)558 ± 4181098 ± 1037
Table 5. Comparison of growth in non-contaminated and metal-contaminated environments of the six-tree species used in the remediation of metal-contaminated sites in the ACK ([40,53] Mujike et al. In press).
Table 5. Comparison of growth in non-contaminated and metal-contaminated environments of the six-tree species used in the remediation of metal-contaminated sites in the ACK ([40,53] Mujike et al. In press).
SpeciesA. auriculiformisA. lebbeckD. regiaL. leucocephalaM. indicaS. guineense
Height (m)14.169.455.214.535.18.76
Diameter (cm)14.268.145.68.525.28.2
Metal-contaminated Environments
Height (m)6.45.53.28.63.06.1
Diameter (cm)8.210.24.910.34.98.4
Table 6. Dynamics of spontaneous herbaceous vegetation between tree species plantation corridors (RA (%): relative abundance, ∆R = difference in cover between measurement dates).
Table 6. Dynamics of spontaneous herbaceous vegetation between tree species plantation corridors (RA (%): relative abundance, ∆R = difference in cover between measurement dates).
SpeciesFamily20212023∆R (%)
Bulbostylis pseudoperennis Goetgh.Cyperaceae8648−38
Microchloa cupricola (Rendle) StapfPoaceae4968.6+19
Imperata cylindrica (L.) P. Beauv.Poaceae1219+7
Celosia trygina L.Amaranthaceae3.26+2.8
Setaria pumila (Poir.) Roem. & Schult.Poaceae2.20.2−2
Teramnus labialis (L.f.) Fabaceae29+7
Ageratum conyzoides L.Asteraceae1.25.8+4.6
Euphorbia hirta L.Euphorbiaceae0.45+4.6
Tithonia diversifolia (Hemsl.)Asteraceae0.21+0.8
Crassocephalum rubens (Jus. Ex Jacq.)Asteraceae00.4+0.4
Cynodon dactylon (L.) Pers.Poaceae01.2+1.2
Nicandra physaloïdes (L.)Solanaceae03+3
Panicum maximum Jacq.Poaceae00.2+0.2
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Langunu, S.; Kilela Mwanasomwe, J.; Nghonda, D.-d.N.; Colinet, G.; Ngoy Shutcha, M. Mineral Condition Changes in Amended Soils and Woody Vegetation Installed on a Polluted Soil with Trace Metals in Lubumbashi (DR Congo): Results of a Four-Year Trial. Environments 2025, 12, 224. https://doi.org/10.3390/environments12070224

AMA Style

Langunu S, Kilela Mwanasomwe J, Nghonda D-dN, Colinet G, Ngoy Shutcha M. Mineral Condition Changes in Amended Soils and Woody Vegetation Installed on a Polluted Soil with Trace Metals in Lubumbashi (DR Congo): Results of a Four-Year Trial. Environments. 2025; 12(7):224. https://doi.org/10.3390/environments12070224

Chicago/Turabian Style

Langunu, Serge, Jacques Kilela Mwanasomwe, Dieu-donné N’Tambwe Nghonda, Gilles Colinet, and Mylor Ngoy Shutcha. 2025. "Mineral Condition Changes in Amended Soils and Woody Vegetation Installed on a Polluted Soil with Trace Metals in Lubumbashi (DR Congo): Results of a Four-Year Trial" Environments 12, no. 7: 224. https://doi.org/10.3390/environments12070224

APA Style

Langunu, S., Kilela Mwanasomwe, J., Nghonda, D.-d. N., Colinet, G., & Ngoy Shutcha, M. (2025). Mineral Condition Changes in Amended Soils and Woody Vegetation Installed on a Polluted Soil with Trace Metals in Lubumbashi (DR Congo): Results of a Four-Year Trial. Environments, 12(7), 224. https://doi.org/10.3390/environments12070224

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